This invention relates to a garage door safety locking system and more particularly to a garage door safety locking system in which the door is automatically and quickly locked against further movement in the event a supporting spring or cable snaps thereby releasing the door.
A typical and common garage door configuration involves the use of a pair of tracks mounted on opposite sides of the door opening and curved to extend back into the garage, with wheels or rollers mounted on the sides of the door to move within the track.
When the door is in its fully open position, it extends back over the opening parallel to the floor. As the door is being closed it begins to develop a downward component of force due to its weight as the track curves downwardly. To prevent the door from crashing down under its own weight while it is in the partially open position, a counter weight is ordinarily provided in which at least one cable is connected at one end to the door and at its opposite end to a spring which is attached to the building frame or track.
The force of the spring is designed to balance approximately the weight of the door to make it easier to raise the door from its closed position and also to reduce the possibility of an accident should the door handle be released before it is fully open or fully closed.
As the spring exerts a more or less constant force over its range of expansion, the force on the door due to its weight tending to bring it down is not normally exactly balanced because this force depends on the position of the door. Thus, where the door is fully closed, the spring force is not adequate to raise it and some lifting effort is required. When the door is partially open at some point, the spring force and the vertical component of the door's weight may be in balance. When the door is open further, spring force may pull the door into its fully open position.
One of the problems with the arrangement as just described is the significant safety hazard should the spring or its connected cable snap while the door is being opened or closed. Garage doors are operated on a daily basis for years without attention or maintenance. Twenty years or more may go by without an inspection of its mechanism, especially when it continues to operate without problems.
It is therefore of no surprise that eventually there may occur a failure of some part of the mechanism. If the failure is in the spring or the connecting cable while the door is being opened or closed, the whole weight of the door, which can be considerable, can be applied to the person who is holding the door handle. If the operator is a child, or even an adult taken totally by surprise, severe physical injury or even death can be caused by the door crashing to its closed position.